Prior to the present invention, pumping installations have been used in which an electric motor or other prime mover, located above ground, drives an axial flow pump, located below ground, through a relatively long drive shaft unit which is several feet in length. The drive shaft unit typically comprises several shafts connected end to end by screw-threaded couplings. In such pumping installations, the drive shaft unit expands and contracts longitudinally with temperature changes and it tends to vibrate transversely. Both of these factors tend to cause malfunctioning or rapid wear at the pump shaft seal, usually because the seal cuts a groove in the pump shaft, with subsequent leakage there. In actual practice, repair and replacement of the shaft seal and the pump shaft has been a major maintenance expense in prior underground pumping installations. Proper operation of the shaft seal is very important because of the presence of foreign particles in the water being pumped.